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The first half of the Solar Impulse round-the-world attempt saw pilot Andre Borschberg break the world record for the longest solo flight. Powered by the sun and welcomed by governments across Asia and beyond, the journey has been one of uplifting successes, technological breakthroughs, tense standoffs and, ultimately, a message of hope that renewable energy can change the world.

pv magazine: Youve come a long way  physically and metaphorically  since the Solar Impulse round-the-world flight began in Abu Dhabi in March. Do you think that people are now beginning to understand the message you are trying to spread?

Andre Borschberg: I think they do. The presence of solar is important, and its the same for applications on the ground  the message is that Solar Impulse is bringing together energy efficiency on one side, and intelligent use of renewables on the other, which of course for us means solar energy.

This message is getting through very well. During the journey we stopped in many countries, and this was an advantage. In some ways it is a dream to make the flight non-stop around the world, but by stopping in various countries it means there are opportunities to interact with people on the ground. We did this extensively in India and China, for example  two large countries that are interested in our project. So the response and the coverage has been excellent.

Some people still argue the line that a solar-powered plane will not be a commercial reality for many decades, so the entire endeavor is pointless. Do you find that this misconception of what you are trying to achieve is still prevalent?

Borschberg: From some people, yes. But the majority understand that this is simply the first step. Since the time of the Wright Brothers and Lindberg aviation has always had to explain that what is feasible in an airplane can be done much more quickly and easily on the ground. So some people still need this explanation, but for others the message is being received clearly.

In China they get it. They are keen on all types of solutions  solar, wind and energy efficiency  to combat the terrible pollution situation they have in the cities right now.

And were you warmly welcomed across China when you were there?

Borschberg: Very much so. We began talking to the Chinese authorities two years ago in order to gain authorization. We were not sure how they would react. Our airplane is very special, we fly very high, and not exactly in a way that a transport airplane flies. We need special regulations and authorizations. And at the same time we wanted to find out if China would be interested in communicating the technology, and they have been. We secured partnerships with official constituencies in China that promote science and technology, particularly clean tech, and they helped to provide contact with the media, and especially CCTV, which is the largest broadcaster in China. This was important.

Abu Dhabi was the launch point, and will also hopefully be the finish point for the successful completion of your journey. Could you explain the role the UAE has played in helping this project come to fruition?

Borschberg: The collaboration with the UAE made sense from two perspectives. One, operationally, because we wanted to cross India and be in China very early in the season. It was the best starting point, and is a good ending point to complete the journey.

Number two, the UAE is extremely active in sustainability and renewable energy and technologies. Masdar is a showcase, but they also invest heavily in research, so it made a lot of sense for us to be there.

Were now here in Paris for the COP21 summit. Speaking more broadly, how can this conference help nurture a wider realization of  not only what is at stake if we do not find ways to use more renewable energy  but also what is feasible?

Borschberg: I am extremely happy to see that everybody agrees about what needs to be done, which was not the case in Copenhagen in 2009. From a political point of view, it is no longer a question of "do we have a problem?" The question now is "how do we move forward?" There have been great partnerships between administrations and private institutions, and that is extremely positive. There is a push, there is no longer a resistance. Now, private institutions are asking governments to do something.

We have a long way to go in terms of keeping temperature increases below 2 degrees. The INDCs pledged wont get us there, and there are a lot of countries that will increase their emissions over the next few years, many of them being the larger countries. So I am worried that time is against us, and the ship has huge inertia and is difficult to turn. It turns slowly. But I am happy with the state of mind.

Youve said that it is hard to convince people to make changes in their behavior. But sometimes  as weve seen with Elon Musks successes with Tesla and the Powerwall  great marketing and a great story can sow the seeds of change. So bearing this in mind, how vital is it that the Solar Impulse mission succeeds?

Borschberg: It is extremely important because we want to show that the impossible is possible. It is a great inspiration for the younger generation. All of the young people we meet look at the airplane with wide-eyes. These guys will make the next steps on this journey. We are simply preparing that path. There is a lot left to learn. We know the world. It is not about discovering new places but new ways to do things. If this project can serve that, inspire the younger generation  just like how I was inspired as a boy to follow my dreams  then its mission accomplished.

The Solar Impulse aircraft is currently undergoing maintenance in Hawaii. Could you talk a little about what type of work has been done on the plane?

Borschberg: The aircraft behaved extremely well and worked extremely well throughout the journey. We had two issues. One, I had an issue with what I call the virtual co-pilot. This software supervises what the airplane is doing when I am resting. This did not work properly. It is a question of the software not being tested enough, but we are working on that. This created some difficulties when I left Japan.

Secondly, when I landed in Japan from China, it was unplanned. And because it was unplanned we didnt have all of our infrastructure on the ground so, after landing, we damaged the airplane. It wasnt serious damage and it was repaired easily, but because there had been repairs we then needed to conduct what is called a maintenance flight, which is normal for any type of airplane.

However, I was unable to do a separate maintenance flight because there is so much traffic in the region where we were, so I had to do it at the same time as I left for Hawaii. So a combination of the maintenance flight and the five days, five nights flight led to temperature increase in the batteries that was over the designed point that we had.

We decided to change the batteries in Hawaii, and thats the reason why we had to stay there. The technology was no trouble at all. It is the matching of the mission profile with the design of the airplane that didnt work out.

And these real world conditions are hard to perfectly model prior to the flight.

Borschberg: Exactly. The departure from Japan was difficult because it was monsoon-type weather. It was difficult to find a good weather window, and reliability of weather forecasts for five days in advance is only 30%, which means a 70% chance that the actual weather we experience is different. Which essentially means that the weather WILL be different from what we are expecting. And that is very hard to deal with.

Is this where you passed the point of no return and had to make the call to carry on, despite what the ground team was saying?

Borschberg: Yes, exactly. That was when the virtual co-pilot did not work and all of the engineers said come back, but I told them I am going to continue.

How did you feel, having to make that call?

Borschberg: It was hard. It was hard because I felt that the team was splitting, which was pretty bad. Some of the engineers threatened to resign. So really, it was a very serious situation. I was very disturbed by this, and there were quite a lot of other emotions to deal with because I knew my family was watching and I didnt know if I had the right to put so much emotional pressure on them. So it was tough.

The live feed with the shark following you was a rather amusing, if morbid touch!

Borschberg: Yes! It is meant to show that failure is not something we want to think about.

On to the solar aspect: have you had to replace any of the cells, or have they performed as expected?

Borschberg: We only had to replace one. We found a small hole in one of the cells; we think somebody dropped something on it. So that is one solar cell damaged out of a total of 17,500 or so, all working perfectly.

That is what we are seeing  the great advantage of solar PV technology. When it is installed, it works! And when it is installed it doesnt cost anything anymore, it just keeps on working, producing electricity. Fantastic! It just keeps going.

Was there any weak link in the system  either technically or perhaps in terms of human fallibility? I understand that the batteries, which overheated, are one of the heavier components of the plane.

Borschberg: You have to realize that we have an extremely complex, experimental airplane that normally would fly over deserts and unpopulated areas so if it comes crashing down it cannot hurt anyone on the ground.

What has been unique for Solar Impulse is that we are allowed  and we asked  to be able to fly over and towards the major cities worldwide. When I left Nanjing I had authorization to fly over the center of Shanghai, and at low altitude in order to take pictures. I mean, this is a forbidden zone! But the Chinese authorities said: "For this, we give our agreement". This is an airplane that is extremely sophisticated in terms of reliability, which explains sometimes why we have some glitches, because complexity brings added risk of something not working. In my case it was the virtual co-pilot, but the basic technology itself  the solar cells, electric motors, batteries  this triumvirate all worked extremely well.

In preparing for the Japan to Hawaii leg, you famously learned how to meditate and rest your body for 20-minute periods of sleep. Did you find that this preparation was enough? Were you surprised by how well, or how badly, your body coped with this record-breaking leg?

Borschberg: It was better than I expected. I could have continued. I flew for an additional eight hours around Hawaii before landing. I could have landed at 10pm but landed at 6am the next morning. I had a lot of things to prepare but it was such a great moment, you cannot imagine. I felt like I was carried by the goodwill of everybody involved in the project, and by my dream and peoples passion for me to succeed. You get this from somewhere  you cannot measure it or explain it  but you feel it, and Im sure it helped me a lot.

On to the next leg of the journey in 2016. Who will be taking the controls in March?

Borschberg: It will be Bertrand. This was the exploration leg. We didnt know if the performance of the airplane was sufficient. We didnt know if we could plan the flight to keep the plane in the right weather conditions, and we didnt know if we could have a sustainable pilot. Keeping the pilot in optimum condition for 5-6 days was a challenge, and it was the leg Ive been thinking about for the last 12 years, so now its time for Bertrand to experience it!

And looking ahead, you land successfully  hopefully  in July, receive the plaudits, take a well-deserved holiday and then where does the Solar Impulse story go after that?

Borschberg: In a lot of directions. Technically we will begin work on an unmanned version, with the aim being to develop an aircraft that can fly into the stratosphere, using solar power of course. This will hopefully be capable of flying above bad weather, so higher than 20 km altitude. For one year we have to build up the experience to either replace or complement what satellites can do. There is huge potential in building solar-powered aircraft that can perhaps perform better than satellites, delivering better information and services, all while being completely sustainable and independent from energy you take from the ground. We are starting to put our engineers to work in this direction.

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The pv magazine editorial team includes specialists in equipment supply, manufacturing, policy, markets, balance of systems, and EPC.

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